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Old 03-28-2008, 10:34 AM   #27 (permalink)
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Originally Posted by tasdrouille View Post
I won't debate the fact that you can get better FE than stock with a CAI, but have you ever tried a WAI?
Yes. I've had 4 warm air intakes from the factory thus far.

Every Volvo up to the late 90s had a thermostatic intake designed to take in air from either in front of the grill or near the exhaust or a combination of the two in order to maintain a minimum 70f intake temp. When the thermostat fails (every single one does after 10 years) it gets stuck in the hot air position and absolutely decimates both fuel economy and power. All 4 of these cars had compression ratios of 9.8-10.7 and a knock sensor. They all got FE numbers between 17-23mpg with the hot air intake, and 21-30mpg with cold air intake. I kept track of every one very meticulously. So have you ever tried a cold air intake?

Originally Posted by Daox View Post
The idea of the WAI is to reduce pumping losses (and increase fuel vaporization in some cases). Since the air is less dense the throttle must be opened further to maintain the same amount of power. This will reduce pumping losses, not increase them.

Yes, warm air will tend to retard timing on some engines. However, on others it won't. It depends on their design and how the engine is tuned. I believe its fairly well known that Saturns react very well to WAIs. Other cars won't. You really just have to try and see if it works.
The pumping losses you describe exist when there is a difference in air pressure between the intake manifold and the and the bottom side of the piston (AKA crankcase). The simple solution if you want to eliminate pumping loss isn't to heat up the intake air but to apply a vacuum to the crank case. A lot or racers do this. I tried it years ago and it work but its too much of a hassle to maintain.
There are very few cars on the road built in the last 20 years without a knock sensor. I don't know if the 1.9 motor in your Saturn has a knock sensor but I would like to see the FE number increase with your warm air intake.
Originally Posted by trebuchet03 View Post
depends how warm - some cars, the temps need to be pretty hot for this to happen.

And explain just why pumping losses increase?

Finally, on the subject of vaporization.... Not on a fuel injected car - that's what injectors do - regardless of temperature Given that the amount of unburnt fuel that leaves the car is less than 1% - this isn't a big issue
I'll give you that, but I haven't seen one warm air intake that doesn't lose more power and efficiency because timing is being retarder than it gains from any pumping loss decrease.

Another point. When Volvos have the thermostat stuck in on the hot air side, they tend to fail smog because of extremely high NOx numbers. Most mechanics don't know how to diagnose this so they end up in the junkyard.


Last edited by tjts1; 03-28-2008 at 10:44 AM..
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